SOS: Bad O2 Sensor, Engine loosing power, stuttering, nearly stalling? (3 Viewers)

Joined
Jul 2, 2019
Messages
51
Location
Connecticut
Hi all. I’m on vacation out of town and the old girl is giving me some trouble. The truck is a ‘94. On my way in to Boston I got a code, pulled over and checked the code. It was a 21, so bad O2 sensor. Didn’t think much of it and honestly don’t know if it’s the cause of the real issue.
As I was driving along, the truck fell right on its face. No power, not really responding to throttle input, but if I put it in neutral and rev it up, it’ll eventually normalize. I tried to find a specialty shop on the area to diagnose, but couldn’t so I dropped it off at the dealer (🙄) who charged me $150 to tell that after a full day of looking at it, they couldn’t find anything wrong except MAYBE some of the distributor wires weren’t in all the way. Tech apparently test drove it and it was fine so I picked it up and the problem has gotten much worse. Won’t accelerate at times, trouble responding to throttle, all the same issues.

I’ve noticed it seems to be less of an issue in higher revs, so I’ve been manually picking gears today. Checked intake hose for cracks and for water in the air filter and distributor cap.

Anyways, I have to drive home to southwestern CT either tonight or tomorrow at 5 in the morning and I really don’t feel like getting stranded. This all seems too weird to be caused by a dead O2 sensor but I did some searching and found a thread about driving with the O2 sensors unplugged, forcing the truck into a default rich state.

Really just looking for some advice here. A 2.5 hour drive home won’t be fun with these issues, but I’m going to have to limp it home somehow now that you can’t ride in the cab with AAA. Any thoughts? I’m all ears.
 
Joined
Jul 21, 2015
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1,924
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Bend, OR
Are you still getting any codes after a CEL reset? Does it idle ok? Is the wiring harness touching the EGR pipe?
 
Joined
Sep 15, 2020
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Spokane
Is the cat blocked? I was getting similar codes and it turned out that one of the bricks in the cat was loose and blocking the exhaust flow.
 
Joined
Jul 2, 2019
Messages
51
Location
Connecticut
Are you still getting any codes after a CEL reset? Does it idle ok? Is the wiring harness touching the EGR pipe?

Yes, codes reappear immediately after restarting the truck even after CEL reset. Idles okay but I can feel a slight misfire. Nowhere near as rough as when driving. I’ll check the harness again but I’m pretty sure it’s not making contact
 
Joined
Jul 2, 2019
Messages
51
Location
Connecticut
Is the cat blocked? I was getting similar codes and it turned out that one of the bricks in the cat was loose and blocking the exhaust flow.
Hmm. Possible, though I can feel it flowing out the back of the pipe. Any way to check?
 
Joined
Jul 21, 2015
Messages
1,924
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Bend, OR
Have you checked the wiring where it connects to the 02 sensor? I've had a short in the 02 sensor wiring there before.

Have you tried running it with the 02 sensors disconnected?
 
Joined
Jul 2, 2019
Messages
51
Location
Connecticut
Have you checked the wiring where it connects to the 02 sensor? I've had a short in the 02 sensor wiring there before.

Have you tried running it with the 02 sensors disconnected?
I haven’t check that yet, and honestly I wasn’t sure if running with the O2 sensors was kosher. I think ‘94s only have them before the cats if I’m remembering that correctly. I might give that a shot once the truck cools down a bit
 
Joined
Nov 20, 2013
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1,040
Location
PA
'94 only has them before the cats. Disconnect both sensors and take it for a drive. It will not hurt anything. Just make sure you strap the wires out of the way. If the truck drive near normal, you have found your culprit. You can then try reconnecting one then the other to determine which is bad.

FWIW, I've driven my '93 with the O2 sensors disconnected for well over 1k miles with no ill effect.
 
Joined
Jul 2, 2019
Messages
51
Location
Connecticut
'94 only has them before the cats. Disconnect both sensors and take it for a drive. It will not hurt anything. Just make sure you strap the wires out of the way. If the truck drive near normal, you have found your culprit. You can then try reconnecting one then the other to determine which is bad.

FWIW, I've driven my '93 with the O2 sensors disconnected for well over 1k miles with no ill effect.

Well, unfortunately that didn’t fix it. Both O2 sensors are unplugged and seemed hopeful for the first 20-25 minutes of my drive home. Stuttering and loss of power issue came back making my 2.5 hour drive home a little harrowing. Pulled off a few miles after damn near stalling but it seems alright for the time being. Just need to make it the final 20 minutes home and I’ll look things over with a clear head tomorrow after work... if it’ll get me to work 😂
 
Joined
Apr 5, 2006
Messages
794
Location
Canyon Lake, TX
Mine (96 LX450) did this stumble then stall today too. But only was when I was in the reverse gear. What gives?!
The first place I would look is if the wire harness is shorting out at the EGR pipe at the back of the engine. When the transmission shifts in reverse, the engine rocks over the opposite direction than when going in forward gear. I would gently peal back the insulation tape on the wireing harness at the pipe, and take a good look at the wires for any that are melted together
 

Proven

RTFM, STEP 6, POST
Joined
Apr 11, 2006
Messages
914
Location
Atlanta
Hi all. I’m on vacation out of town and the old girl is giving me some trouble. The truck is a ‘94. On my way in to Boston I got a code, pulled over and checked the code. It was a 21, so bad O2 sensor. Didn’t think much of it and honestly don’t know if it’s the cause of the real issue.
As I was driving along, the truck fell right on its face. No power, not really responding to throttle input, but if I put it in neutral and rev it up, it’ll eventually normalize. I tried to find a specialty shop on the area to diagnose, but couldn’t so I dropped it off at the dealer (🙄) who charged me $150 to tell that after a full day of looking at it, they couldn’t find anything wrong except MAYBE some of the distributor wires weren’t in all the way. Tech apparently test drove it and it was fine so I picked it up and the problem has gotten much worse. Won’t accelerate at times, trouble responding to throttle, all the same issues.

I’ve noticed it seems to be less of an issue in higher revs, so I’ve been manually picking gears today. Checked intake hose for cracks and for water in the air filter and distributor cap.

Anyways, I have to drive home to southwestern CT either tonight or tomorrow at 5 in the morning and I really don’t feel like getting stranded. This all seems too weird to be caused by a dead O2 sensor but I did some searching and found a thread about driving with the O2 sensors unplugged, forcing the truck into a default rich state.

Really just looking for some advice here. A 2.5 hour drive home won’t be fun with these issues, but I’m going to have to limp it home somehow now that you can’t ride in the cab with AAA. Any thoughts? I’m all ears.

Do you know how old the O2 sensors are? have you changed them already to test behavior?

Is the only code you are getting the one related to O2 sensors?

This could be a bad ground or a harness issue like others have mentioned. A "hot bed" for issues is the wire bundle behind the EGR valve which may not have had adequate heat shielding. Usually that was fuel injection related if I remember right, but still it is something to look at.
 
Joined
Sep 2, 2020
Messages
76
Location
Bay Area, CA
Well, unfortunately that didn’t fix it. Both O2 sensors are unplugged and seemed hopeful for the first 20-25 minutes of my drive home. Stuttering and loss of power issue came back making my 2.5 hour drive home a little harrowing. Pulled off a few miles after damn near stalling but it seems alright for the time being. Just need to make it the final 20 minutes home and I’ll look things over with a clear head tomorrow after work... if it’ll get me to work 😂
I have a 93 and literally went through all of this. Replaced both 02 Sensors, EGR valve, Knock sensors and their connectors (27yrs old, so...) The true loss of power was found by the Knock sensor connector issues, as well as a plugged up muffler which I also replaced. Power is back now. I hope this and this diagram help out, noting the location of the location of 02 and Knock sensors.

1608105032136.png


Please let us know how things worked out and the culprit!
 
Joined
Sep 2, 2020
Messages
76
Location
Bay Area, CA
I have a 93 and literally went through all of this. Replaced both 02 Sensors, EGR valve, Knock sensors and their connectors (27yrs old, so...) The true loss of power was found by the Knock sensor connector issues, as well as a plugged up muffler which I also replaced. Power is back now. I hope this and this diagram help out, noting the location of the location of 02 and Knock sensors.

View attachment 2526016

Please let us know how things worked out and the culprit!
Almost forgot to add, I noticed still a little bit of power loss and finally found that the EGR to Vacuum solenoid vacuum hose fell off somewhere, so I would not discount a vacuum leak either. :)
 
Joined
Jul 2, 2019
Messages
51
Location
Connecticut
I have a 93 and literally went through all of this. Replaced both 02 Sensors, EGR valve, Knock sensors and their connectors (27yrs old, so...) The true loss of power was found by the Knock sensor connector issues, as well as a plugged up muffler which I also replaced. Power is back now. I hope this and this diagram help out, noting the location of the location of 02 and Knock sensors.

View attachment 2526016

Please let us know how things worked out and the culprit!

Thank you!! I’ll be sure to check the knock sensors as well. The EGR shouldn’t be an issue as it’s plugged and bypassed. Thankfully we don’t have emissions for a vehicle this old in Connecticut.
 
Joined
Sep 2, 2020
Messages
76
Location
Bay Area, CA
Thank you!! I’ll be sure to check the knock sensors as well. The EGR shouldn’t be an issue as it’s plugged and bypassed. Thankfully we don’t have emissions for a vehicle this old in Connecticut.
You're welcome! Yeah, CA sucks when it comes to emissions.
 

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